Within the construction industry, slab on grade construction is the most common form of concrete construction for structural buildings. As the name suggests, a slab is a single layer of concrete, several inches in thickness. The slab is typically poured thicker at the edges to form an integral footing with reinforcing rods used to further strengthen the thickened edge. The slab may rest on a bed of crushed gravel to improve drainage. Slab on grade is commonly used in residential, commercial and industrial building construction applications.
When using slab on grade construction, there is often a need to set interior form boards within the monolithic concrete slab. Interior forms are needed to establish varying elevations within the slab, such as between a garage and the living space of a house in a monolithic slab design. Interior form boards are additionally used to establish slab depressions for shower pans or to accommodate localized interior floor covering materials such as stone, tile or pavers. Interior form board are also used to provide a control line as a means to hang anchor bolts and seismic hold-down bolts at interior load bearing and shear walls.
When form boards are utilized in the construction process, the boards are rigidly fixed in place prior to pouring the concrete slab. Accordingly, the form boards must be securely fixed in position so that the weight and the pressure of the concrete, when poured, will not displace them. Close tolerances are required for this process and only a very small margin of error is acceptable. As such, the most common method of fixing interior form boards in place is by driving wood or steel stakes securely into the subgrade and then securing the form boards to the stakes in the desired configuration. Commonly, two types of stakes are utilized to secure the form boards in place. First, vertical stakes are installed to hold the form boards in line and to elevation. Second, brace stakes are driven into the ground at approximately a forty-five degree angle and nailed to the vertical stake or form boards to hold it in line against the lateral pressures of the concrete. The stakes are then removed after the concrete is poured and just after it has reached its initial set, at a point where the forms boards will hold their shape without being displaced by the weight or pressure of the surrounding concrete, but while the concrete has a viscosity that will allow it to consolidate into voids.
Inherent to the concrete slab on grade construction process is the problem of moisture migration through the slab from the underlying soil. Adverse impacts of excess moisture in the slab include adhesion loss, warping, peeling, unacceptable appearance of resilient flooring, deterioration of adhesives, ripping or separation of seams, air bubbles or efflorescence beneath seamed continuous flooring, damage to flat electrical cable systems, buckling of carpet and carpet tiles, offensive odors, and growth of fungi. Moisture migration through soils and concrete slabs on grade not only creates a problem for the performance of floor covering and coating systems, but can also contribute to indoor air quality issues. Moisture beneath floor coverings or within adhesives or carpets can provide an environment suitable to further microbial development, adversely affecting indoor air quality.
Additionally, it is possible for other hazardous materials, such as radon gas, benzene, asbestos or other soil gases present in the underlying soil to migrate through the concrete slab. It is desirable to prevent the migration of these hazardous materials through the concrete slab because they are known to adversely affect indoor air quality and safety.
To reduce the amount of moisture and to control the migration of hazardous materials, an effective vapor barrier, vapor retarder or waterproofing membrane is typically installed beneath the concrete slab. Vapor barriers are often placed on the subgrade beneath the concrete slab to minimize vapor and soil gas transmission through the concrete slab. The vapor barrier serves to block or slow down the transfer of moisture and gases from the ground into the concrete slab, thereby reducing the devastating effects on floor coverings that promote mold and fungi growth and reducing the exposure of the interior environment to harmful gases. Vapor barriers are typically sheeting materials based on polyethylene or polyolefin technology. Spray-applied vapor barriers are also available such as Liquid Boot® from CETCO. LIQUID BOOT® Membrane is a cold, spray-applied membrane used in the construction industry that provides an impermeable barrier against vapor intrusion into structures. Spray-applied vapor retarding material is typically spray-applied directly onto the prepared subgrade or spray-applied onto a geotextile fabric with is first positioned to cover the prepared subgrade. In slab on grade construction, the vapor barrier or retarder is placed on top of the subgrade. As directed by the ASTM (American Society for Testing and Materials) Designation: E 1643-98 Standard Practice for Installation of Water Vapor Retarders used in Contact with Earth or Granular Fill Under Concrete Slabs, it is desirable that the vapor retarder be positioned to lap over footings or seal to the foundation wall, or both, and seal around penetrations such as utilities and columns in order to create a monolithic membrane between the surface of the slab and moisture sources below the slab and at the slab perimeter. The ASTM also provides guidelines for the protection of the vapor barrier against damage during installation of reinforcing steel and utilities and during placement of concrete. In accordance with the ASTM guidelines a damaged vapor retarder should be repaired with vapor barrier material or as instructed by the manufacturer by lapping beyond the damaged area a minimum of 6 inches and sealing as prescribed for sheet joints. Damage to the vapor barrier that is not repaired, increases the moisture and hazardous gas exposure of the concrete slab, thereby increasing the risk of problems associated with excessive moisture in the slab and harmful gases in the interior environment.
In the slab on grade construction process, vapor barriers are installed or spray-applied over the subgrade and before any interior form boards are placed. Accordingly, when the wood or steel stakes used to support the form boards are driven into the subgrade, the vapor barrier is invariably punctured. Since these stakes are not removed until after the concrete is poured and sufficiently set, it is not possible to repair the stake hole punctures in the vapor barrier. In addition, concrete contractors using hand screed equipment to place and level concrete customarily use screed pins which are merely round steel stakes driven vertically through the vapor barrier into the subgrade in order to support the screed bar. The screed pins penetrate the vapor barrier and leave holes when removed.
Because punctures in the vapor retarder can significantly increase water-vapor emissions through concrete floor slabs, efforts have been made to minimize the damage to the vapor barrier. It is known in the art to apply a layer of sand or a granular layer over the vapor barrier to reduce the possibility of damage due to machinery and foot traffic. In is also known in the art to specify a thick vapor retarder that will be more puncture-resistant during typical construction activities. The ASTM indicates that the use of stakes driven through the vapor retarder should be avoided because they puncture the vapor barrier, leaving a hole which cannot be repaired after removal of the stakes because the resulting hole is under the surface of the concrete slab. In an effort to satisfy this requirement, solutions have been provided that allow for the placement of support structures for form boards that do not puncture the retarder, such as a pad-and-post support for slab edge forms. However, these support structures are inadequate to be used to support interior forms boards because they are not securely fixed in place. They are unstable and unable to support the weight and pressures of the concrete and therefore the form boards to not hold their shape as required. The prior art does not describe a means for maintaining the integrity of a vapor barrier utilized during the construction process of the slab on grade foundation.
Accordingly, what is needed in the art is an apparatus and method to maintain the integrity of the vapor barrier when utilizing form board support stakes or screed pins, which are removed after the concrete slab has been poured. Additionally, a need exists in the art for an apparatus and method to secure support structures used in slab on grade construction that is capable of withstanding the pressure and weight of poured concrete.